Properties of a Yeast Cytochrome P-450-Containing Enzyme System which Catalyzes the Hydroxylation of Fatty Acids, Alkanes, and Drugs

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65977/1/j.1432-1033.1973.tb02948.x.pd

AEROBIC BIODEGRADATION OF AN OXYGENATES MIXTURE: ETBE, MTBE AND TAME IN AN UPFLOW FIXED-BED REACTOR

Abstract}Aerobic degradation of ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and tertamyl methyl ether (TAME), as tertiary-substrates, was studied in a continuous upflow fixed-bed reactor (UFBR) using an external oxygenator and sintered glass rings as biomass carriers. The UFBR has been shown to be an effective system for the simultaneous and continuous long-term degradation of the threeoxygenates mixture as sole source of carbon and energy. Therefore, the oxygenates feed concentration must be related in conjunction with the hydraulic retention time ''HRT'' and vice versa. The permissible feed concentration of both MTBE and TAME to achieve more than 99% removal efficiency is about 80 mg L À1 at a constant HRT of 24 h. The same performance can be obtained if the HRT kept at a value equal or above to 15 h for a feed concentration of about 80 mg L À1 of both MTBE and TAME. However, the ETBE removal efficiency was always greater than 99% whatever the ETBE concentration feed (between 10 and 100 mg L À1 at a constant HRT of 24 h) and the HRT (between 24 and 13 h at a constant concentration feed of about 80 mg L À1 ) tested in this study. The highest ETBE, MTBE and TAME removal rates achieved throughout the UFBR runs, with efficiency better than 99%, were 140 AE 5, 132 AE 2 and 135 AE 2 mg L À1 d À1 , respectively. No metabolic intermediates including tert-butyl alcohol (TBA), tertbutyl formate (TBF) and tert-amyl alcohol (TAA) were detected in the effluent during all the reactor runs. Furthermore, based on the chemical oxygen demand balance, all the removed oxygenates were completely metabolized. The results of this study suggest that the higher resistance to biodegradation exhibited by the MTBE and the TAME is probably due to the steric hindrance for the attacking enzyme(s); and the major limiting step to the oxygenate degradation maybe the accessibility and the cleavage of the ether bond, but not the assimilation of their major metabolites such as TBA, TBF and TAA. These results were concomitant with the batch tests using the reactor's immobilized biomass as inoculum.

Electronic properties of mixed lithium-oxygen clusters

Herein electronic structure as a function of cluster size has been probed through ionization potentials measurements in order to derive general trends in the evolution of the structure and stability of lithium oxide clusters LinOm. The structural evolution was investigated by varying progressively the oxygen rate in order to observe transitions from the metallic Lin to the ionic structure (Li2O)n. We have demonstrated that this structural transition splits into three specific ranges. This result, in contrast with the general behavior observed with other electronegative elements combined with alkaline or alkaline-earth metal clusters, but similar to what is known about BanOm and CsnOm, constitutes a signature of a specific role played by the oxygen atoms when included inside a metallic cluster

Ionization potentials and geometrical structure of pure and oxygenated barium clusters

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Plasmon spectroscopy and chemical structure of small bimetallic Cu(1-x)Agx clusters

cited By 11International audienceThe optical properties of small Cu-Ag bimetallic clusters have been experimentally and theoretically investigated in relation to their chemical structure analyzed by high resolution transmission electron microscopy (HRTEM). Cu (1-x)Agx clusters of about 5 nm in diameter are produced in a laser vaporization source with a well-defined stoichiometry (x = 0, 25, 50, 75, and 100%) and dispersed in an alumina matrix. Absorption spectra are dominated by a broad and strong surface plasmon resonance whose shape and location are dependent on both cluster composition and sample aging. Detailed modeling and systematic calculations of the optical response of pure and oxidized mixed clusters of various chemical structures have been carried out in the framework of classical and semiquantal formalisms. Optical and HRTEM measurements combined with theoretical predictions lead to the conclusion that these bimetallic clusters are not alloyed at the atomic scale but rather present a segregation of chemical phases. Most likely, they adopt a Cu@Ag core-shell configuration. Moreover, the nanoparticle oxidation process is consistent with the formation of a copper oxide layer by dragging out inner copper atoms to the cluster surface. © 2015 American Chemical Society

Electronic properties of mixed barium–oxygen clusters

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